Two-way radios have become popular communication tools where phones or other communication methods are not cost effective or simply not efficient. These 2-way radios generally allow users to communicate with one another without experiencing interruptions caused by other users, such as the case with citizen band radios.
Early two-way radio systems relied on the voice of one of the users to call or gain the attention of a fellow user. As improvements were made to these systems, a call feature was added. The call feature would notify the user of an incoming communication by producing an audible tone.
In many instances, an audible tone is ineffective in getting the attention of the intended receiver. Since two-way radios are often used in environments such as construction sites where there is a great deal of noise, users often miss calls and important messages.
In other instances, the receiver may not want the audible tone to alert others of incoming messages. When the receiver is in a quiet area such as a library, church, movie, or other area where audible disturbances are unwelcome, the receiver would have to turn off the two-way radio or risk causing a disturbance.
Because audible annunciation methods in two-way radio communication systems are often undesirable, a need has developed for a method of alerting a two-way radio user of an incoming call which does not produce an audible tone.